TS ONTC 200/900 f4.5 Carbon tube TS-Optics 200mm/8" ONTC f/4.5 Newtonian (carbon tube) · R8RO · ... · 29 · 1155 · 4

Andy Wray:
Interesting:  you are not changing things much ... a 200PDS with its coma corrector is exactly the same focal length.  What are you hoping to gain?

I don't think the supposed "superior optics" is going to matter a lot for AP, once you're diffraction limited you'd hit the buffer. Why do you think you are going down in focal length with the TS GPU? AFAIK isn't reducing the focal length at all and there is no extra light gathering power even if it did.

I don't think the supposed "superior optics" is going to matter a lot for AP, once you're diffraction limited you'd hit the buffer. Why do you think you are going down in focal length with the TS GPU? AFAIK isn't reducing the focal length at all and there is no extra light gathering power even if it did.

This was in response to Andy's question. He said I would be at exactly the same focal length, which is not true 900≠1000. Me going down in focal length would be from my 1000/200 F5 scope to a 900/200 F4.5 scope. This would also give me a bit more light gathering capability compared to my current scope. 

As for superior optics, I am talking about the quartz coating, 97% reflectivity, bigger secondary and Strehl graph and certificate.

Hi,

After using a 200 PDS for years I upgraded to this exact telescope. 

I use mainly for deepsky imaging with an ASI294MM (23.1 mm diagonal). The telescope is very thermally and mechanically stable. It is carried well by my EQ6-R and would probably sit on a HEQ5 too. Judging from the output, the mirror must at least be of acceptable quality.

The only thing I wished I had included from the start is a screw-threaded focuser (it came with a cheap focuser and I changed it to a Moonlite CR2 which also lacks threading). Exactly what focuser you should go for will depend on your coma corrector of choice. I can elaborate on this if you want.

I personally went for CNC rings and 2x Losmandy dovetails. This may be an overkill, the scope is rather light. But it will enable you to load the setup with heavy accessories.

Have a look at my recent pics for some information to base your decision on. I recently started using a Paracorr 2 which seems to be a perfect fit, it lands me at about f/5.1 (the mirror is actually slightly faster than f/4.5). I personally would avoid the GPU due to its vignetting.

Alternatives may be an 8" in the TS UNC series or Skywatcher 190MN, but I have not owned any of these myself. From what I read they are all of good optical quality, but lower mechanical quality than the ONTC series. UNC scopes are also less versatile when it comes to changing the primary mirror position to adapt to different coma correctors/planetary imaging/visual. Another alternative may be the similar ONTC 10" f/4.

My last image: https://www.astrobin.com/k8l808/B/

Uncropped test data from yesterday (there is some vignetting in the corners from the 1.25" filters which are slightly too small).



Mounted in the basement:

Andy Wray:
Just food for thought:  I'm also thinking about a long term upgrade for my 200PDS and am yearning after the Takahashi Epsilons.  I won't make the move though until I know I've made the most out of my 200PDS which I certainly haven't yet.

I have had major issues with my current Skywatcher scope to the point that I no longer want to spend twice the money it costs on trying to get it to work as I want.

andrea tasselli:
Andy was saying it because with the SW CC there is a a focal reduction at play. It is still the same aperture no matter how you cut it and the difference in reflectivity is trivial (94% vs 97% I believe).

There would be no way for me to know that since he didn't specify what CC he was using and I was simply going of my own experience with the TSGPU

andrea tasselli:
If there is SiO2 coatings (the blurb doesn't say) most if not all modern mirrors out there have it. The substrate is equivalent to Pyrex so no quartz there. I had bad experience with OOUK coatings, very bad ones too so buyers beware. A bigger secondary you can get one yourself if you're so inclined (but you lose a bit of light gathering area there). As for the certificate I wouldn't put my money on it being 100% accurate, besides making no difference in actual practice. And if you really need one I can provide you one free of charge.

I am well aware that the aperture won't change. As I mentioned in my first response, it would simply be a nice plus. My main reason for upgrade would still be for the far better build quality, customization options, carbon tube and mirror mountings. I have had major issues with my current Skywatcher scope to the point that I no longer want to spend twice the money it costs on trying to get it to work as I want. So I instead opt for an upgrade, hence the initial topic, which we have strayed from.

I have ordered a Steeltrack myself, together with a threaded adapter for the Paracorr 2 to see whether I can gain collimation stability. However I am yet to receive it so I can't judge its quality. Nor do I know anything about the focuser TS recommends to you

Not sure why they recommended just this one but I think it's because of the fact that I have the TSGPU and it apparently plays nicely with the threads on that corrector. We'll see, like I said: I have not yet decided. But if you do end up getting first light with the Steel Track before I buy mine, please report back!

Reg Pratt:
10" ONTC here. I went with the 2" Feather Touch focuser paired with a Sesto Senso 2 motor. To date I have not had to use any backlash compensation for autofocus. Also am not experiencing any tilt or flexure issues with the compression ring and TSGPU coma corrector. Coming from Moonlite focusers I was concerned about not being threaded to the drawtube but it hasn't been an issue at all. The primary mirror clips were a bit loose but took very little effort to tighten. Its been a workhorse for the 4 months I've had it. Holds collimation no problem when I leave it mounted.

I previously had 2 steel tube GSO F4 Newts and while they worked for the most part there was a lot of mechanical issues ( to be expected form cheap scopes). There's none of that nonsense going on with the ONTC. Thing is built like a tank and even at 10" its very light. I'm of the opinion that the carbon tune does make a difference. Not only does it make the scope a good deal lighter but it also cools very fast. I usually have my scope uncovered within an hour or 2 of night and there are many nights where autofocus may only run once or twice. I've had nights where it didn't run again after the initial run (NINA triggers AF after a 10% HFD increase).


When I was looking to get into newts I didn't feel there was a whole lot to choose from for a higher quality scope. I considered OOUK but read some less inspiring things about them. In this price range I don't think you will find a better scope than the ONTC. The last handful of images on my profile were made with it if you're interested.


Side note: Mine has GSO mirrors as is the default for UNC and ONTC scopes. TS does sometimes take OOUK parts and put them into their own carbon tube though. I know someone who had a 12" with OOUK optics and as far as the mirrors themselves were concerned the quality was good. In either event I agree that the you're not going to gain much from the optics over your SW. What you will gain is vastly superior components and having dealt with cheaper newts I can tell you that it makes a very big difference. I don't have to fiddle with things. I don't have to trouble shoot. I unpacked the scope, put it together, collimated, and use it. That's it.